Signal sources, for example path or rotary angle tranducers which provide output signals representative of a distance traveled by an element or a rotary deflection of a shaft usually provide a signal which is representative of a reference point or, typically, a zero point. The output signal which represents this reference or zero point must be calibrated, so that the deflection of the transducer from the zero or reference point can be accurately determined by reference to the transducer signal. Calibrating and adjusting the zero point is costly and, particularly if the transducers are made under mass-production conditions, may require individual adjustment on many elements due to manufacturing tolerances. Calibrating mass-produced transducers, thus, and later on maintaining the adjustment during operation, is a continuous and costly problem.